The present invention is an apparatus that electrically grounds a disc drive spindle by providing an electrical pathway from the rotating disc drive spindle to the chassis. In particular, the invention discharges an electrical charge from disc in a magnetic disc drive system.
Magnetic disc drives act as mass storage devices for computers by selectively polarizing portions of a magnetic disc surface. In the continual drive to increase the storage capacity of magnetic disc drives, the density of data stored on the disc has been continually increased by decreasing the size of the polarized portions of the disc surface. Reduction in the size of the magnetically polarized bit positions on the disc results in a decrease in the signal strength induced in the read/write head as the surface of the magnetic disc passes under it. Accurate data transfer to and from the disc requires minimizing extraneous signals, or electronic "noise".
The magnetic disc typically rotates at speeds of up to 5400 revolutions per minute and is supported by a spindle. Both are driven by a spindle drive motor. In the process of rotation, considerable static electrical charge is built up on the disc and spindle. An electrical pathway to eliminate static charge must be provided. The static elimination system, itself, must not generate interfering noise.
Prior art static elimination systems rely upon a cantilevered arm spring loaded against the side of a rounded spindle shaft end. At the point of contact with the spindle shaft, a contact area contacts on the loaded spring arm. The material of the contact area is selected to enhance wear and electrical continuity characteristics. Problems with these designs include vibration, fluctuating continuity, and high resistance (about 20 K .OMEGA. to 5 M .OMEGA.). All of these problems exacerbate the generation of electrical noise through the recording head and spindle drive bearings. This noise presents a potential barrier to the recording density achievable through thin film heads and magnetoresistive heads. Elimination of static charge without the attendant noise in conventional spindle grounding designs is necessary to increase information density on the disc.
In the cantilevered design of the prior art, the spring loaded arm typically has a resonant frequency of oscillation in the audible range. The energy input due to the rotation of the drive spindle causes the cantilevered spring arm to vibrate at its resonant frequency. Damping, or otherwise changing the frequency response of the spring has had limited success. Cantilevered designs also require a greater amount of space for the cantilevered arm. In addition, the resonance of the arm can alter the flying height of the head which changes the signal strength of the readback signal.
A disc drive having an inexpensive reliable contact to a drive spindle which provides improved frequency response and electrical continuity would be a significant contribution to the art.